Vacuum degassing apparatus for molten metals



Oct. 14, 1969 E. BREUER VACUUM DEGASSING APPARATUS FOR MOLTEN METALS,Filed Jan. 27, 1967 2 Sheets-Sheet 1 Fig. 1

Erich Brewer l md $1 M W W Oct. 14, 1969 BRE E 3,472,503

VACUUM DEGASSING APPARATUS FOR MOLTEN METALS I Filed Jan. 27, 1967 2Sheets-Sheet Erich Brewer United States raemomce H 3,472,503 Patentedot.'14, 1969 Int. Cl. C21c 7/10,- Hb 3/52 US. Cl. 266-34 1 ClaimABSTRACT OF THE DISCLOSURE A vacuum degassing apparatus for meltedmetals, particularly steel, includes a vessel in which the degassingtakes place, the upper portion of the vessel including a vacuum g'astakeoff space and one or more electrically heated rods for maintainingtemperature of the melt during the degassing phase. The melt itself isnot poured into the degassing vessel until the vacuum has beenestablished, and enters the top of the vessel through a tubularconnection piece associated with a supply tank for the melt such as aconverter. As the melt discharges from the lower end of the connectionpiece, the flow widens out in a funnel-shaped manner in the form of aspray which facilitates release of the gas from the melt. The tubularconnection piece through which the melt flows into the vessel iselectrically conductive and serves as one current supply contact to theresistance heating rods which are secured at the inner ends to theconnection p1ece.

FIELD OF THE- INVENTION The present invention relates to the art ofvacuum degassing melted metals and is particularly concerned with animprovement in the construction of the degassing vessel which minimizesthe tendency of the molten metal to splash against and adhere to thevessel walls.

DESCRIPTION OF THE PRIOR ART It is known to degas melted metals,particularly steel, by subjecting them to the effects of a vacuum in aclosed vessel. The gas which escapes from the melt causes a splashing ofthe liquid steel whereby the splashes can partly reach the refractorylining of the vessel. Since the degassing operation takes some timeduring which the temperature of the melt sinks appreciably (for instance30 to 50 C.), splashes of metal can easily adhere to the lining of thevessel. These particles of steel which adhere to the lining have adetrimental effect on the efficiency of the degassing process. In orderto prevent the melt from cooling during degassing, it is known toprovide heating resistors, particularly graphite resistances, underneaththe cover of the vessle. With such an arrangement the liquid steel isintroduced through the bottom of vessel. The gas bubbles which occurwhen the degassing operation is undertaken with such an arrangementresult, however, in a considerable amount of splashing. To prevent theheating device from becoming inoperative after a short time it isnecessary to have a considerable empty space above the level of the meltin the vessel. This necessitates a large heating power and aconsiderable overall height for the vessel, this being a disadvantageparticularly when the device has to be used in connection withcontinuous casting plants which already are of a considerable height.

The relatively large heating power makes it necessary to cool thecontacts of the graphite rods which have been used up to now for theheating, the cooling water coming within close proximity of the meltchamber.

There is therefore a considerable danger that in the event of a leak,water may enter the vacuum chamber containing the melt.

SUMMARY OF THE INVENTION The object of the invention is to achieve afundamental improvement as regards degassing devices of the aforesaidtype. It has been found that when a stream of liquid metal falls into avessel evacuated to a pressure of about 0.8 torr, it immediately spreadsout in a funnel-shaped manner and forms a spray consisting of finelydivided drops. When this descending fog impinges on the surface of themelt no appreciable splashing occurs.

In order to utilize this phenomenon in a degassing apparatus, it isnecessary to provide an arrangement so that the degassing action isalready effective when the melt flows from the storage vessel into thecrucible-like pouring vessel.

In a degassing apparatus of this kind for liquified metals, particularlysteel melts, comprising a cruciblelike ladle with a cover-shapedheadpiece containing an electrical resistance heating device, an openingis provided for filling in the melt which on the one hand is invacuum-tight communication with, the ladle and on the other hand withthe storage vessel for the liquified metal in such a manner that thecloseable outlet in the storage vessel is above the filling opening inthe covershaped headpiece.

A particularly expedient form of degassing apparatus in accordance withthe invention is obtained when an electrically conductive andinterchangeable connection piece is provided which is inserted in theopening of the cover headpiece and extends down into the interior of thecrucible-type ladle and serves for filling the melt into the ladle andalso acts as a current supply contact for at least one heatingresistance which passes from the connection piece through the wall ofthe cover headpiece in a radially outward direction.

BRIEF DESCRIPTION OF THE DRAWINGS A constructural example of theinvention is shown in the drawings where FIG. 1 is a longitudinalsection and FIG. 2 a cross-sectional view along the plane A-B of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to thedrawings numeral 1 indicates a crucible-like ladle and 2 is thecover-shaped headpiece. An electrically conductive tubular connectionpiece 5 to which the heating resistances 3 are connected is inserted inan opening 4 which is expediently located in the middle of theheadpiece. The resistances 3 extend outwards through the wall of thecover-like headpiece and are pressed resiliently against theelectrically conductive connection piece 5 by means of a device 13equipped with a press bolt or spring. The lower, discharge end of theconnection piece 5 thus extends below the position of the heating rods 3so as to prevent damage to the latter by the molten metal. Outside theheadpiece, the resistances are connected by way of vacuumtight bushingsand current leads 10 to a current supply. Water cooling devices 11 servefor cooling the contact points.

In the example shown, there are three heating resistances 3 which arearranged in a starlike formation with respect to the connection piece 5and are supplied with three-phase current. A larger number ofresistances, namely a multiple of three, can also be provided. Naturallyit is also possible to provide only a single resitsance, but this isobviously not so expedient.

The heating rods are preferably made of graphite or a similar resistancematerial. Connection piece 5 can also consist of the same material.

The upper part of the crucible-like ladle is enclosed by an airtighthood 8 with projections 8a for the resistances, these projections beingprovided with covers 8b. Inside the hood 8 above the connection piece 5there is an opening which is closed by a fusible cover plate 9. A pipeconnection 7 is provided for the purpose of evacuating the hood and thusalso the interior of the crucible-shaped ladle. A flange 80 with a sealenables the storage vessel 14 to be mounted on the hood 8 in avacuum-tight manner and so that the opening 15, which can be closed by aplug, is in alignment with the connection piece 5. The connection piece5 which is used for pouring in the melt, can be provided with aremovable tubular insert liner 6 consisting of head resistant material,e.g., refractory material, for instance zirconium oxide.

A device 12, shown schematically, serves to discharge the ladle. Theheight of the apparatus should be selected so that the melt when itemerges from the connection piece 5 and passes into the vacuum forms afunnel-shaped stream which expands as it passes downwards butpnactically does not come into contact with the sides of the vessel.

The apparatus functions in such a manner that after evacuation by way ofthe pipe connection 7, the discharge opening of the storage vessel, forinstance a converter filled with melted steel, is opened. After thecover plate 9 has melted, the liquid metal passes through the connectionpiece 5 into the crucible-shaped ladle where the flow widens out in afunnel-shaped manner as indicated by the broken lines and in the form ofa spray already releases a large part of the enclosed gas.

The apparatus possesses the advantage that it is easy to operate in aquick and reliable manner, and at the same time is very compact. Theconnection piece 5 in the headpiece moreover provides the possibility ofinserting a gas or oil burner as a supplementary heating device fordrying and heating the apparatus or holding its temperature.

I claim:

1. Vacuum degassing apparatus for liquefied metals, particularly steelmetals, comprising a crucible type ladle having a cover-shapedheadpiece, said headpiece containing at least one electrical resistancetype heating element in rod form extending radially inwards through thewall of said headpiece, said headpiece being provided with a fillingopening communicating said ladle with a storage vessel so located that aclosable discharge opening in said storage vessel is above the fillingopening in said headpiece, hood means enclosing said ladle in avacuum-tight manner, means for evacuating said head, an interchangeabletubular connection means located within said opening in said headpieceand which extends into the interior of said ladle to a level below saidheating rod, said tubular connection means serving for filling saidladlewith melt from said storage vessel and being constituted by an innertubular member made from a heat-resistant material and an outer tubularmember in heat-transfer contact with said inner tubular member, saidouter tubular member being made from electrically conductive resistancematerial, and said outer tubular member being connected to the inner endof said resistance type heating rod so as to electrically heat saidinner tubular member.

References Cited UNITED STATES PATENTS 2,133,235 10/1938 Slayter;3,014,255 12/1961 Bussard et al. 266-344 3,125,440 3/1964 Hornak et a1.266-344 X 3,137,566 6/1964 Thieme -49 X 3,384,362 5/1968 Philbrick266-344 X FOREIGN PATENTS 1,192,368 10/1959 France.

I. SPENCER OVERHOLSER, Primary Examiner R. D. BALDWIN, AssistantExaminer U.S. Cl. X.R. 13-33

